Page:Popular Science Monthly Volume 43.djvu/651

culminating point in the yellow, and descends toward both ends of the spectrum; it exactly corresponds with the curve of assimilation of carbon by plants under variously colored light. It is also remarkable that the green color of the pupa is only obtained by yellow light, or by such green as contains yellow; such is, as known, the average color of leaves. We thus have a case where environment itself makes the color which approximately matches it. The meaning of these researches is self-evident. No naturalist will probably attempt to explain the animal colors and markings without the aid of natural selection. But it becomes less and less probable to admit that the animal colors are a result of a selection of accidental variations only. The food of the organism, and especially the amount of salt in it, the dryness or moisture of the air, the amount of sunshine, and so on, undoubtedly exercise a direct effect on the color of the skin, on the fur, and on the very intimate anatomical structure of the animal. As to the relative parts which must be attributed in the origin of each separate variation to natural selection on the one side, and to the direct action of environment on the other side, it would simply be unscientific to trench uj)on such questions in a broadcast way, so long as we are only making our first steps in discriminating the action of the latter agency. The first steps already indicate how complicated such questions are, especially in those cases where natural selection must act in an indirect way—not as a mere selection of already modeled forms, but as a selection of forms best capable to respond to the requirements of new conditions—in which case the intimate organization of the living being comes in the first place. All we may say at the present moment is that the direct modifying action of environment is very great, and that no theory can claim to be scientific unless it takes it into consideration to its full amount.—Nineteenth Century.

 

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Mr. W. Roe, of the Cape Colony, has pointed out a disadvantage connected with irrigation. Most water used for the purpose contains variable (quantities of soluble salts, some of which are not taken up largely by plants. Every application of water, therefore, adds to the saline ingredients of the soil—a very different effect from that of excess of rain water, which, so far as there is open subsoil for it to drain away, would be likely to take out rather than add to the soluble salines in the soil. The mischief of the accumulation of salts in the soil is aggravated in a dry-air land where evaporation is great. The air, acting like a sponge on a surface, takes up the water, leaving the accumulated salts in the surface soil. But this surface soil is as the sponge to the layer beneath. Constantly after each water-leading, the water is drawn to the surface and evaporated, leaving the accumulated salts in the surface soil. The harm done by this accumulated salt will depend on the nature and quantity of the salines in the water used, as also upon the quantity of water supplied.